Definitions—(a) Wireless medium (WM): The medium used to implement the transfer of protocol data units (PDUs) between peer physical layer (PHY) entities of a wireless local area network (LAN); (b) Station (STA): Any device that contains an IEEE 802.11-conformant medium access control (MAC) and physical layer (PHY) interface to the wireless medium; (c) Access Point (AP): Any entity that has a station (STA) functionality and provides access to the distribution services, via the wireless medium for associated STAs; and (d) Beacon Frame: A Beacon frame is one of the management frames in IEEE 802.11 based WLANs. It contains all the information about the network. Beacon frames are transmitted periodically to announce the presence of a Wireless LAN network. Beacon frames are transmitted by the Access Point (AP) in an infrastructure BSS. In IBSS network beacon generation is distributed among the stations. For example, a Beacon frame can include a MAC header, Frame body and FCS and have fields including a timestamp field, a beacon interval field which is a time-interval between beacon transmissions, and capability information field which can span 16 bits and contain information about capability of the device/network.
The IEEE (Institute of Electrical and Electronics Engineers) 802.11ah specification framework as defined in the Specification Framework for TGah, 802.11-11/1137r12 (https://mentor.ieee.org/802.11/dcn/11/11-11-1137-12-00ah-specification-framework-for-tgah.docx) prescribes support for 2 MHz channel bandwidth with 64-FFT (Fast Fourier Transform), which may reuse most of the physical layer (PHY) designs of the 20 MHz mode defined in the IEEE 802.11ac specification framework IEEE P802.11ac/D4.1-Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications—Amendment 4: Enhancements for Very High Throughput for Operation in Bands below 6 GHz (http://www.ieee802.org/11/private/Draft_Standards/11ac/DraftP802.11ac_D4.1.pdf) by downclocking the operations by a factor of 10 (or by “10×”).
For example, for small battery-powered sensor type of devices or stations (STAs), the system clock speed of an 802.11ah-based STA may be downclocked by 10× so that power consumption and cost of the STA may be reduced. Such downclocking, however, may result in an increase by 10× of a received packet processing delay time (aRxPLCPDelay). Accordingly, a time duration associated with a short interframe space (SIFS), i.e., the time interval between receiving a data frame at a STA and transmitting an acknowledgement (ACK) frame for the received frame from the STA (e.g., as defined in the IEEE 802.11 specification), may have to be proportionally increased. For instance, due to 10× downclocking in a sensor STA, a typical aRxPLCPDelay equal to 12.5 μs for 802.11ac 20 MHz mode may jump 10 times to around 125 μs for an 802.11ah-based communication, and similarly, a typical SIFS duration equal to 16 μs for 802.11ac operation may increase to around 160 as for the 802.11ah-based communication.
In other cases, however, e.g., for a relatively high data rate application such as a cellular offloading application throughput related to the media access control (MAC) layer is important and it may be preferable to have a shorter SIFS duration. The SIFS time may be reduced by increasing the speed of the system clock. For example, using 5× downclocking (instead of 10× downclocking), aRxPLCPDelay may be decreased from 125 μS to 62.5 μS, and accordingly, the SIFS time may be shortened to approximately 80 μS. The requirements for a high data rate application of a cellular device is in contrast with the requirements of a small low-power sensor device, which may not need to improve throughput, or to use the double clock speed as that may increase cost and power consumption of the sensor device.
To support the two different types of applications (i.e., high data rate and low data rate) under the IEEE 802.11ah specification, an existing technique proposes two downclocking levels. For example, for channel access operations and for small battery-powered sensor STAs (and its application) operating under the IEEE 802.11ah standard, the system clock may be downclocked 10 times to achieve a SIFS duration that is 10 times higher the IEEE 802.11ac level—this SIFS configuration is referred to as “regular SIFS.” Further, for more capable devices such as STAs operating under IEEE 802.11ah standard and implementing or executing a cellular offloading application, the system clock may be downclocked 5 times to achieve a SIFS duration that is 5 times higher the IEEE 802.11ac level—this SIFS configuration is referred to as “short or small SIFS.” Accordingly, the small SIFS configuration relates to or defines shorter time duration than a regular SIFS configuration.
This proposed technique, however, requires that the STA receiving data packets or frames from an associated STA or access point (AP) informs the associated STA or AP how fast it can respond to a packet reception with an acknowledgement (ACK) frame, i.e. whether the STA supports the short SIFS for shorter response time or the regular SIFS for a longer response time. Based on this information provided by the STA, the associated STA or AP may set a correct waiting period in which an ACK frame is anticipated (e.g., “ACKTimeout” value) after which period the STA may begin packet retransmission.
Another shortcoming of the proposed technique is that, under the STA-informed SIFS scheme, one or more third-party STAs, which receive the data packet sent by the AP but do not receive the ACK frame, may not be able to ascertain the time instance or period indicating the end of the packet exchange between the packet-receiving STA and the AP. In some embodiments, the third-party STAs are not able decode the MAC header in the data packet exchanged between the AP and the STA. Due to this ambiguity in terms of the end of the packet exchange, the third-party STAs may (untimely) attempt to access channel, as such resulting in a channel contention scenario.